(a) Field of the Invention
The present invention relates to a cutting apparatus for a noncircular cross section for machining a workpiece having a noncircular cross section such as a piston for an internal combustion engine, an outer circumferential surface of which has a noncircular cross section.
(b) Description of the Prior Art
Heretofore, in order to work a workpiece having a noncircular cross section, a profiling machining process using a master cam has often been utilized. Such profiling machining process has several disadvantages, for example, it is necessary to use the master cam, the manufacture of which requires much time and cost. Further, the configuration of the master cam which can be formed is restricted to a certain allowable extent because of its peculiar problem of making the master cam, and therefore it is impossible to form the workpiece to an optional configuration.
Furthermore, since a follow-up characteristic of a profiling machining device is restricted, the workpiece is limited in the increase of its relating speed, and thus it is impossible to drive the device at high speed, and therefore it is difficult to shorten a cycle-time.
In some instances, an outer diameter cutting process by NC-control without using the master cam is utilized. This process is possible at low speed, however, it is impossible at high speed. That is because, in a hydraulic servo-system, a response characteristic of a servo-valve is low and thus a response speed of a hydraulic cylinder can not be increased. Further, the control of the oil temperature is difficult and thus the response characteristic of the cylinder is changed owing to the variation of the oil temperature. On the other hand, in a system utilizing the servo-motor, the servo-motor is frequently changed or reversed in its rotational direction, and thus the response characteristic of the servo-motor can not be improved because of various factors such as inertia of the motor, elastic deformations of a ball screw and of a feed table.
It is an object of the present invention, therefore, to provide a cutting apparatus for a noncircular cross section in which the above-described various disadvantages of the prior art are eliminated, that is: the problem of the follow-up characteristic as in the conventional profiling machining device can be eliminated. the workpiece can be rotated at a high speed to be subject to a high speed cutting operation; the cycle-time of the machine can be substantially decreased; any configuration of the workpiece can be machined the change of the configuration of the workpiece can easily be accommodated by said apparatus; and high accuracy of working can be maintained for a long time.